1. Field of the Invention
The present invention relates to a servo signal recording apparatus capable of recording a servo signal to a magnetic tape, and more specifically relates to an information recording apparatus capable of recording a variety of information to a magnetic tape while performing tracking servo control based on the servo signal recorded on the magnetic tape. In particular, the present invention relates to a learning-type optimum notch filter control system adaptable to a data storage system for a computer, and also relates to a recording and reproduction apparatus capable of implementing such a learning-type optimum notch filter control system.
2. Description of Related Art
Magnetic tape has a variety of applications such as audio tape, video tape, and computer tape. Particularly in the field of data backup tapes, magnetic tapes with a recording capacity of 800 GB (giga byte) or more per reel have been commercialized following increases in the capacity of hard disks for backup. High capacity backup tapes have been proposed with the development hereafter of techniques for backing up data exceeding 4 TB (tera byte).
One conceivable method of increasing the capacity of magnetic tape is, for example, to make the magnetic tape thinner to increase the tape length per reel, without increasing the reel diameter of the magnetic tape per reel. Another method involves shortening the recording wavelength of data recorded on the magnetic tape to increase the longitudinal recording density of the magnetic tape. A further method involves reducing the recording track width of the magnetic tape to increase the lateral recording density of the magnetic tape (high recording density technique).
When the recording track width is reduced by employing a high recording density technique for magnetic tape, the magnetic head is unable to accurately follow the recording track due to the lateral motion of the magnetic tape during data recording or reproduction, or the like. If the magnetic head is unable to accurately follow the recording track, errors are more likely to occur in writing information to the magnetic tape or in recording information from the magnetic tape. In view of this, currently, systems that are provided with a servo system using a servo signal recorded to a magnetic layer or a back-coat layer of the magnetic tape during manufacture have become mainstream.
As for servo systems, there is a magnetic servo system and an optical servo system. With the magnetic servo system, a servo signal is magnetically recorded to a magnetic layer of the magnetic tape, and the servo signal is magnetically read to perform servo control. With the optical servo system, a servo signal constituted by a recessed array is formed on a back-coat layer on the magnetic tape with laser irradiation or the like, and the recessed array is optically read to perform servo control.
These servo systems enable the magnetic head to follow the recording track when recording data to a magnetic tape or reproducing data from a magnetic tape, even when the magnetic tape moves laterally relative to the magnetic head. Specifically, the servo signal recorded on the magnetic tape is firstly read with a servo head. Then, according to the read servo signal, the position of a head unit (which includes at least a data recording head and a data reproducing head) along the width of the magnetic tape is controlled so as to allow the data recording head or the data reproducing head to follow the recording track. This enables information to be recorded to the correct position on a magnetic tape, and information recorded on a magnetic tape to be correctly reproduced.
Disclosed in Patent Document 1 (JP H8-30942A) and Patent Document 2 (U.S. Pat. No. 6,226,688) are timing based servo systems. With these timing based servo systems, the servo signal is a pattern that is at an angle relative to the width direction of the magnetic tape. An apparatus compatible with such timing based servo systems confirms the head position from the time intervals between the peaks of the reproduction waveform when the servo signal is reproduced.
Disclosed in Patent Document 3 (JP 2004-86959A) are a difference detector and a set value modification unit. The difference detector detects a difference between the resonance frequency of the head actuator and the center frequency set in the notch filter. The set value modification unit modifies the set value of the center frequency in the notch filter, based on the difference detected by the difference detector.
However, a problem with the techniques disclosed in Patent Documents 1 and 2 is that a PES (position error signal) must be of a lesser amplitude when the recording track width is narrowed following an increase in the information recording density of the magnetic tape. Patent Document 3 discloses a technique for reducing the resonance frequency of the actuator with the notch filter but does not disclose a technique for reducing other factors such as periodic noise, narrow-band noise, and the like.